A patient support apparatus includes a mattress that defines a plurality of grooves. A bladder is disposed within each groove. Each bladder is operable between a deployed state and a non-deployed state. A flap is disposed adjacent to each groove. Each flap includes a broad contact surface and a narrow contact surface. A manifold is in fluid communication with each bladder. The manifold is configured to direct fluid into each bladder to adjust the bladders between the deployed state and the non-deployed state, and consequently move the flaps between a raised position and a lowered position, respectively.